At a court hearing Sunday, prosecutors requested a five-year sentence for embattled ex-businessman Alexei Kozlov.
Dozens of supporters wore white ribbons at the hearing to show support for Kozlov, who is accused of fraud. His supporters say the trial is a corrupt scheme by a former business partner.
During an anti-government rally Saturday, participants called for people to attend the proceedings to support Kozlov and his wife, prominent journalist Olga Romanova, RIA-Novosti reported.
Many supporters heeded the call, flooding the courthouse and spilling out onto the street.
During a live blog of the proceedings, news agency Rapsi said on Twitter that people at the courthouse cried "shame!" in reaction to the prosecutor's demand for a five-year sentence.
Kozlov's trial resonates with many who see it as a symbol for government-sanctioned corruption.
The former businessman also writes a blog on Slon.ru about his experiences in prison. That has given greater visibility to his case, making him one of the most well-known prisoners in the country.
He contends that the case was fabricated by one-time business partner and former Federation Council Senator Vladimir Slutsker.
Kozlov was originally sentenced to eight years in prison on charges of illegally obtaining shares in Iskozh, a company headed by him but controlled by Slutsker's Finvest holding.
In September 2011, the Supreme Court overturned the verdict and ordered a retrial.